Rotary spark gap modulator



July 29, 1952 H. J. WHITE ROTARY SPARK GAP MoDuLAToR Filed Oct. 30, 1945 4 Sheets-Sheet 1 E m p l mm; Wm N H f A ww. N IV Tl //l um WA M l1 l m July 29,

Filed Oct. 50, 1945 H. J. WHITE ROTARY SPARK GAP MODULATOR 4 Sheets-Sheet 2 FIGB sTEADY-STATE voLTAGE STEP-UP INVENTOR HARRY J. WHITE ATTORNEY July 29 1952 H. J. WHITE 2,605,310

ROTARY SPARK GAP MoDuLAToR Filed Oct. 30, 1945 4 Sheets-Sheet 3 INVENTOR HARRY J. WHITE ATTORNEY H. J. WHITE ROTARY SPARK GAP MODULATOR July 29, 1952 4 Sheets-#Sheet 4 Filed Oct. 30, 1945 LoAo k65 E T n HA E co mm P ou NO v\ J DISCHARGE PolNT VOLTAGE mor -f TRANsFoRMER coNoENsER VOLTAGE FIG. I2

INVENTOR. 'HARRY J. WHITE ATTORNEY Patented July 29, 1952 ROTARY SPARK GAP MoDULA'roR` Harry J. White, Cambridge, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application October 30, 1945, Serial No. 625,664

20 Claims. 1

This invention relates to modulators, particu,- larly those in which a circuit is provided through which a pulse forming network is charged from a source of alternating voltage and then discharged to pulse a transmitter. A spark gap is used to eiectively connect the line for charging from this source and when the line is charged or later to eiectively connect it for discharging through any suitable load.

It is an object of this invention to provide a circuit for charging a capacity in a pulse forming network.

It is, a further object of thisy invention to provide a circuit for charging a capacity in a pulse forming network and controlled by a spark gap.

Itis a further object of this invention to provide a circuit` either resonant or non-resonant to: the frequency of the voltage source, which will substantially increase the voltage which would otherwise be applied to charge a capacity inV a pulse. forming network.

Other and further objects will appear during the course of the following description.

In very'high frequencyA circuits where the electromagnetic output is pulsed, a magnetron is usually employed as a source of high frequency energy. To trigger or pulse this magnetron. a relatively high voltage in the neighborhood of ten or twenty kilovolts, depending on the char* acteristics of the particular magnetron, is. necessary. This voltage is applied to the magnetron during the entire period of oscillation. It is characteristic. of' magnetrons that if this voltage falls appreciably from rated during the oscillation period,y modes; of oscillation other than the one desired may` result. This causes serious loss of power, lowered magnetron efficiency', and difficulties in tuning, since4 unwanted frequencies are present in the output. Therefore, the. triggering voltage must'. arise. rapidly, remain constant duringv theY oscillatingperi'od', and; decrease rapidly tozero at theend. Inotherwords, an energizing` voltage of rectangular wave. form is desirable.

This energizing voltage or pulse may be obtained from the discharge of a pulse forming network. Such a network consists of electrical elements: so proportionedf and arranged as to st-imulatev the characteristicsof an open circuited uniform line of electrical length equal to one haii. the pulse. duration. It ordinarily comprises a. capacity whichV stores energy from` the source and a soz-called pulse forming line which shapes' the; pulse when the energy stored in the capacity passesf through the. line., This network is.

alternately. charged and discharged". by suitable switching. In the instant disclosure a spark gap is used. To obtain a discharge pulse of high voltage from this network, it is necessary that the line be chargedA to a high voltage, ordinarily, twice the voltage necessary to pulse the magnetron. This requires a high voltage source of energy with the inherent disadvantages of such a voltage. The present invention incorporates .a circuit betweenthe network and the source which substantially reduces the voltage required bythe source and yet charges the network to full. voltage. necessary to pulse the magnetron. This circuit operates in cooperation with the spark gap. It will now be described in more detail in conjunction with the accompanying drawings where:

Fig. 1 is a circuit diagram useful in explaining the theory of this invention;

Figs.2, 3 and 4 are charts of certain waveforms obtainable from Fig. 1;

Figs. 5, 6, 7, 8, 9, 10 and 11 are eachadiagram of an embodimentv of the invention; and

Fig. 12 is a chartv of certain waveforms obtainable from Fig. 11.

In the diagram in Fig. 1 an inductance L and a capacity C` are connected in series with an alternating source of voltage of peakr value E; The period T of the alternating voltage and the inductance and capacity are all of such magnitude as to provide a series resonant circuit. The relationship between these three values may be expressed. by the equation When. the alternating voltage E of waveformA as shown in the upper portion of Fig. 2 is n.13-, plied to the inductance andl capacity the transient by means of which the voltage across condenser C changes from the initial condition to the steady state is shown in the lower portion of Fig. 2 by the full line followed by the broken line. In the casel where there is no dissipation the condenser voltage continues to alternate withY an ever-increasing amplitude. With the damping as provided by load R the peaks do not linearly increase as shown in the Fig. 2 but increase exponentially toward a limiting. valueV which is the steady state peakv alternating voltageY across the condenser. Ii the load R- represents a magi netron, the energy storedin condenser C may be" used to pulse this magnetron by closing switch S when this transient has been allowed to proceed for one-half, one, or two cycles, or more, and then opening switch S when condenser C has substantially discharged'. The variationof; the.

voltage: in condenser C for one-cycle charging:

is shown by the full line in the lower portion of It may be noted that the actual values depend on the resistance of load R, and the values shown are merely representative of loads likely to be encountered in practice.

For the case of non-resonance, that is where the damped natural or characteristic angular frequency of the charging circuit is not equal to the frequency of the applied alternating voltage, f

there is still a voltage gain across the condenser over the applied alternating voltage, if the transient is limited to one or two cycles duration. This gain may even exceed that for the resonant case. The voltage gain for the non-resonant case, especially when the timing is rather far off resonance, may be thought of as being due to the phenomenon of beats, the beats occurring between the steady-state voltage of angular frequency w and the transient voltage of angular frequency g. The voltage rises to high peak values for a few cycles and then subsidies to the steady-state value as the transient dies out. In the resonant case, on the other hand, the voltage rises to higher and higher peak values, the steady-state value being limited in magnitude only by damping.

It is clear that, in general, damping cannot be important in the non-resonant case. An exception must be made for the case of near resoresonance frequency of the charging circuit. This is for the case where the condenser is allowed to charge for one cycle of the applied i voltage. It is seen that maximum step-up ratio for this case is about 3.7 and occurs when is .70 as compared with a value of about 8.1 when 9 is unity. It is to be emphasized that this result is only for one cycle of charge. The steady state value of the step-up ratio is shown by the dotted line, and with no dissipation has a value of iniinity when is unity. The phase angle is represented by the dot and dash line. and in order to have the voltage across the condenser rise to this maximum value in one charging cycle it is necessary to have the applied voltage in the proper phase relationship at the time of opening switch S. For maximum value of the step-up ratio the phase angle will be about 21 degrees.

In Fig. 4 is disclosed as a full line the condenser voltage transient for maximum step-up ratio over one charging cycle, which is of a time duration equal to the period of the applied wave. This is only for the case where g is .70. The impressed alternating voltage is shown by a dotted line.

In the embodiment in Fig. 5 a source of alternating voltage ID, usually 400 cycles, is impressed on a transformer I I The output of transformer Il is connected in series with an inductance I2 and a capacity I3. A spark gap II is provided having a fixed electrode and a rotat-able wheel having a plurality of electrodes evenly and circumferentially spaced thereon. Each rotating electrode passes sufficiently close to the fixed electrode to permit the separating air to break under` the influence of the voltage existing thereacross at the time of passing, and thus form a low resistance path for discharge of any energy which may be stored in condenser I3. After the rotating electrode passes the iixed electrode the arc is broken, to be reformed upon the arrival of the succeeding rotating electrode. It is thus seen that the spark gap I'I operates as a switch. Pulse forming line I4 is in series with condenser I3. This line may be a Guillemin line as shown. Load I5 completes the series circuit.

The wheel of spark gap I1 is preferably mechanically linked with the rotating member of alternating voltage source I0 as shown by dotted line I6. This provides for the shorting of the spark gap at any desired rate with respect to the frequency of the impressed voltage and further for this shorting to occur in any desired phase relationship with respect to the applied voltage wave.

The values of inductance I2 and capacity I3 are chosen to permit either resonant or nonresonant charging therethrough as desired from an applied voltage of known frequency. Spark gap I1 is so mechanically linked as to be driven from the rotating member of source I0 at a rate and phase such that condenser I3 will charge for the desired time depending on whether condenser I3 is to be resonantly or non-resonantly charged and then discharged through the then shorted spark gap to energize load I5 during part or all of the shorted period.

While pulse forming line I 4 is in series with inductance l2 and condenser I3 during charge, it does not have any appreciable eilect on the charging. The frequency of the impressed volt- -age is low in comparison with any resonant frequencies of this line. The inductances of this line oifer a very low impedance at the frequency of the voltage impressed. Furthermore, the condensers of this line do not acquire any appreciable charge, except when the line is discharging.

The embodiment in Fig. 6 is similar to that in Fig. 5 except that the spark gap and charging condenser are reversed in position. The operation is similar to the preceding embodiment. When the gap is opened condenser 23 charges in accordance with its capacity and the inductance ofitnductnrnz. .The a:rmlcieiiscrdischarges when theifgapis shortcrcuitedtorenengize loaidfithe vtime :ofdisehargeiis the cycle dependington'the rate of rotation and the phasingofthe -wheel of 'gap '21A .In lthis embodiment .the voltage source is""not'feiective1y disconnected during the discharging'pf thefcondenser asin thegpreceding embodiment.

n ithe embodiments'hown .inxrFig J7 Vfa spark gap .':generallyfindicated by'numerail 3B `is 1employed .having a vrotary disc 531 through Awhich extendsa plurality Tof peg' type electrodes :such asx and v46. Disc BJ .rotates .a denite relationship 'with'. thefrotatng l.element "of source 30 'toprovidefforchargng fand .at theprcper time `vinfiihe cycle iof the alternating voltage. r`(Londenser'33 is .charged through Vthe circuit formed fwhen i one of i the 'peg"relect1'odes,

say *40, is v disposed in "alignment withiiixed'electrades '41 l'and 42. At .raiflater time :after vtt'ri's charging ^circuit is broken another .of the Jpeg electrodes, lsay SL46, is aligned 'with electrodes' 43 and `1M to form a circuitifor:fdischargeof .condenser Y 33 v through line 34 land; load .35. :Itis .to be -noted 4vthat `the ycharging ltimefof condenser 33 ismore limited than inlpreceding'cazsesdue to theshort time that peg'electr-ode :ll'isi'a'ligned with the electrodes-M and'fto form a-circuit. Hencev the time constant of V'the charging :circuit formed by inductance-32 condenser Mermet be relatively small. `I'Ifhis' is obtainedibyimakmg inductance=32 small. Thislembodimen-t has the advantage of slightly .higher .emcienx:y, since tliesouroeI of power 'isvneverfconnected'whenthe load is 'being pulsed by the network.

The embodiment in 8 'is -somewhat.'simi-lar to 'thatdisclosed in ".Fig. y5. The 'F'igv ment is particularly useful' where ther load .which may be a fmagnet-ron "has its `'output .connected to ani-antenna, and the' antenna is separated fby a Aconsiderable distance vfrom the Apower "units which include source' 50A and transformeriiin the drawing. Long `radio frequency lines r'tend "to make a magnetron unstable #and should 'be avoided if possible. Likewise transmission "of high voltages overy extended ydistances where equipment "of this nature lis likely tobe yused is undesirable. 'These diiiic-ultiees are vrevercortie here by forming thel pulse asin previous embodiments, but at relatively low ffv'oltage, A'and *transi lstic impedance of the coaxial'line. iTo'fmatch the line tothe load and also tostepfthe relatively low voltage pulse'up toa `useful value, alpi-ilse transformer 5B is nsertedbetween the-output of the coaxial linean'dV theload. y

In the embodiment of Fig. '91 three condensers 63a, 6312, and 53e are charged viripeuallei 'and discharged in series :by the Vlswitching :action f of three rotary spark gaps Elm-61h; and 61e mechanically linked togetherv and" to' voltage source'f `Aas shown by dotted line'GG. These threefspark gaps open and close their respective-circuits insynchronism. When'the circuits across the-gapsfare open, condensers 63a, G3b,-and 63C 'are either resonantly or nonresonantly Acharged V'as desired from'source 60. When the spark gaps close their respective circuits these condensers discharge in series, the charge voltage across -f eachbeing additively applied through 'line 64 'to load t5. This is 'possible since inductors 68, G9, 10 vv"and 1| aresubstantially short circuits to thecharging current and substantially fopen circuits Jto 6 the ldischarging current. This Ais l'due tothe frequency components ofthekdischarging current being much .higher ythan lthe .frequency fcom'poments ofthe ch'ang-ing'curre'nt. Obviously1 this circuit is not restricted in use to three groups of storage condensersV and spark rgaps. -Any numberfofgroupspf `c'on'densers and spark -gaps may be used wthithe inductors properly arranged. Theftemibodiment in Rig-.10 :shows Aaniadditional vcrmrlienser vand spark :gap Mgroup 'added to fthe precedingembodim'ent.

.11n the -Vcmboriim'ent inrFig.. 11 1.a diodeI 88 Slis inserted inseriesrwitnithe koutput-cf 'transformer 8i. sincei'thesre'sistancel'of.diode asis vnegligible during 1 'the i positive voltage L wave, condenser 83 willfcharge to'. a'theoreticalvalue' of 7:. V ,rE

during the `positive `cycle of the voltage from transformer 8l. Thisrise of thef4 ch'arge'of condenser 83 is shown in Fig. 12 `"Wliiclris similar in this/respect 'to Fig.2. `On 'the negative cycle o-ff theftransformer voltage lcondenserB vis unable modications.

'Although in all r-embodiments the inductance (i2 in Fig. 5) wl'iasbeen shown separate from the transformer, it is to be understood that this nductance in all embodiments y'may be incorporated' in the transformer as leakage induct'ance to Y'eliminate any 'external inductanca and the terml in'ductance as used inthe claims includes this leakage inductance.

'Numerousaddi'tional applications of the above disclosed 'principles of the invention willv occur to tho'seskilled in the 'art and no attempt has been ma'dehereto' exhaust suchi possibilities. The scope lof thein'vention is dened in thefollo'wing claims.

I claim:

1.jA 'pulse generator, 'comprising `means for storing f electrical energy. .means r for 'forming `a pulse, and a switch alternately connecting said energy storing means to"a source 'of 'alternating voltage `to permit "energy to Abe 'stored therein. and connecting said 'energy storing means through said ,p'ulse'lformingfmeans to a load to permit said stored energy to be 'discharged through said pulse forming means and vto be impressed vas vapuls'e 'on said load, the action of'said 'switch seing synchronized with them# quency of said alternating voltage.

2. A pulse generator comprising, a source of alternating Voltagefacapacity for storing electrical energy, an inductance, a pulse "forming line, a load and va rotary spark-gap, said rotary spark vgap-alternately connecting said capacity and `finductance in Vseries with said source to permit said capacity 'to `charge 'from 'said source and connecting said capacity in series Wilthfsaid pulse forming line `and said load to permit said'capacity to discharge through saidA pulse forming line kand vsaid load, the magnitudes offsaid capacity and inductance being so 'related that said capacity charges to a maximum value during the time of connection to said source, and the motion of said rotary spark gap being synchronized with the frequency of said alternating voltage.

3. A pulse generator, comprising an inductance and a capacity, the magnitudes of said inductance and capacity being such as to form a resonant circuit when connected in series across a source of alternating voltage, a pulse forming line, a rotary spark gap having a rotating disc and a plurality of peg electrodes extending therethrough, said peg electrodes when rotated with said disc alternately connecting said capacity and said inductance to said source of alternating voltage to permit said capacitance to resonantly charge to a maximum Value and connecting said capacity' to said pulse forming line to permit said capacity to discharge through said line whereby a pulse may be impressed on a load connected to said line.

4. A pulse generator, comprising an inductance and a rotary spark gap in series and adapted to be connected to a source of alternating voltage, a capacity and pulse forming line connected in series to the junction of said inductance and said spark gap, said spark gap acting alternately to permit said capacity to charge from said source and to permit said capacity to discharge through said line when said capacity is charged to a desired value to present a pulse at its output, a coaxial cable connected to the output of said line, a pulse transformer having its primary connected to the output of said coaxial cable and its secondary adapted to be connected to a load whereby the load may be matched to the cable andthe voltage of the pulse at the secondary of the transformer may be increased.

5. A pulse generator comprising, an inductance, a diode and a rotary spark gap in series and adapted to be connected across a source of alternating voltage, a capacity and pulse forming line connected in series through a load across said gap, said spark gap acting alterl nately to permit said capacity to charge from said source and to permit said capacity to discharge through said line when said capacity is charged to a maximum value to vimpress a pulse on said load, said diode being so poled as to permit A 6. A pulse generator, comprising a rst capacity and a first inductance in series and adapted to be connected across a source of alternating voltage, a second inductance, a second capacity and a third inductance connected in series across said rst capacity, a spark gap connected from the junction of said first inductance and said iirst capacity to the junction of said second capacity and said third inductance, a second spark gap and pulse forming line in series and effectively connected to the junction of said second inductance and said second capacity, said spark gaps being operable in synchronism to alternately present high impedances to permit said capacities to charge in parallel from said source and when said capacities are charged to a desired value to present low impedances to permit said capacities to discharge in series through said line to impress a pulse on. a load connected thereto, the magnitudes of said second and third inductances being such as to be substantially a short circuit to the charging current' and substantially an open circuit to the discharging current.

'7. A pulse generator comprising, a capacitor, an inductor, a source of alternating voltage seria-ily connected to said inductor, the magnitudes of the inductance and capacitance of said inductor and capacitor being such that said inductor land'capacitor are adapted to form a resonant circuit at the frequency of said alternating voltage when said capacitor is connected across said inductor-and said source of alternating Voltage, a pulse forming line, a load serially connected to said pulse forming line, and a rotary spark gap for alternately completing first and second circuits, said first circuit being isolated from said second circuit, said first circuit comprising said capacitor connected across said inductor and said source of alternating voltage, said second circuit comprising said capacitor connected across said line and said load.

8. A pulse generator comprising a capacitor, an inductor, a source of alternating voltage serially connected to said inductor, the magnitudes of the inductance and capacitance of said inductor and capacitor being such that said inductor and said capacitor are adapted to form a resonant circuit at the frequency of said alternating voltage source when said capacitor is connected across said serially connected inductor and source of alternating voltage, a pulse forming line, a load serially connected to said pulse forming line, and a rotary spark gap having a rotating disk and a plurality of peg electrodes extending through said disk, said peg electrodes when rotated with said disk alternately connecting said capacitor across said serially connected inductor and source of alternating voltage to permit said capacitor to charge resonantly toa maximum value and connecting said capacitor across said serially connected pulse forming line and load to permit said capacitor to discharge through saidline whereby -a pulse is impressed on said load.

9. Apparatus as defined in claim 8 wherein each of said peg electrodes is parallel tothe axis of rotation of said disk and wherein the rotary motion of said rotary spark gap issynchronized with the frequency of said alternating voltage.r Y

10. A pulse generator comprising, an inductor, a source of alternating voltage, a rotary spark gap, said inductor and said rotary spark gap being serially Aconnected across said voltage source, a capacitor and a load, said capacitor and said load being serially connected across said rotary spark gap, said rotary spark gap being synchronized With the frequency of said alternating voltage source for alternately charging said capacitor and discharging said capacitor through said load When said capacitor is charged to a desired value.

1l. A pulse generator comprising, a source of alternating voltage, an inductor, a rotary spark gap, said inductor and said rotary spark gap being serially connected across said voltage source, a capacitor, a pulse forming line, and a load, said capacitor, said pulse forming line and said load being serially connected across said rotary spark gap, said rotary spark gap acting alternately to permit said capacitor to discharge through said pulse forming line when said capacitor is charged to a desired Value whereby a pulse is produced across said load.

12. Apparatus as defined in claim 11 wherein the motion of said rotary spark gap is synchronized with the frequency of said alternating Voltage.

13. A pulse generator comprising, a first capacitor, a first inductor, a second inductor, a source of alternating voltage, said first capacitor, said first inductor and said second inductor being serially connected across said source of alternating voltage, said iirst capacitor being connected between said first and second inductors, a third inductor, a second capacitor, a fourth inductor, said third inductor, said second capacitor and said fourth inductor being serially connected across said first capacitor, said third inductor being connected directly to said rst inductor, said fourth inductor being connected directly to said second inductor, discharge means connected between the junction of said iirst inductor and said rst capacitor and the junction of said second capacitor and said fourth inductor, second discharge means, a load serially connected to said second discharge means, said load and said second discharge means being connected between the junction of said third inductor and said second capacitor and one side of said voltage source.

14. Apparatus as in claim 13 wherein said first and second discharge means are first and second spark gaps.

15. Apparatus as in claim 13 wherein said first and second discharge means are first and second rotary spark gaps synchronized with the frequency of said alternating voltage source.

16. A pulse generator comprising, a network, said network having n capacitors and lL-1 first rotary spark gaps, n being any integer greater than one, said first rotary spark gaps and said capacitors being serially connected so that each rst rotary spark gap is connected between two of said capacitors, there being 2n successive capacitor terminals in said series arrangement, n-l first inductors, one of said first inductors being connected between each pair of successive even-numbered capacitor terminals, considering said capacitor terminals as being numbered from 1 at one end of said capacitor-rotary spark gap series arrangement to 2n at the other end, 11.-1 second inductors, one of said second inductors being connected between each pair of successive odd-numbered capacitor terminals, a source of alternating voltage, a third inductor, said source and said third inductor being serially connected across the capacitor between the first and second of said capacitor terminals, a second rotary spark gap, a pulse forming line, and a load, said second rotary spark gap, said pulse forming line and said load being serially connected across said capacitor-rotary spark gap series arrangement, said rst and second rotary spark gaps being synchronized with the frequency of said alternating Voltage source.

17. A pulse generator comprising, a plurality of capacitors and a like plurality of rotary spark gaps serially connected in alternating fashion beginning with one of said capacitors and ending with one of said spark gaps, a pulse forming line and a load serially connected in the order named to said one spark gap, a different plurality of inductors, connected one each between corresponding plates of adjacent ones of said capacitors, a source of alternating voltage and a charging impedance serially connected across said one capacitor, said rotary spark gaps being synchronized in rotation with the frequency of said alternating voltage source.

18. A pulse generator comprising, a pulse forming line and a load serially connected, a plurality of capacitors and a plurality of inductors, a source of alternating voltage connected in series with a charging impedance, a plurality of rotary spark gaps synchronized in rotation with the frequency of said alternating voltage source arranged to permit said capacitors to be resonantly charged in parallel through said charging impedance from said source and to be discharged in series through said pulse forming line when each of said capacitors is charged to a desired value whereby a pulse is produced across said load.

19. A pulse generator comprising, a capacitor, an inductor, a. source of alternating voltage, a pulse forming line, and a rotary spark gap synchronized in motion with the frequency of said alternating source, said rotary spark gap alternately permitting said capacitor to charge through said inductor from said source and to discharge through said pulse forming line when said capacitor is charged to a desired Value whereby a pulse may be formed at the output of said line.

20. A pulse generator comprising, a capacitor for storing electrical energy, an inductor, a course of alternating voltage, the magnitude of the inductance of said inductor being such as to form a circuit resonant at the frequency of said source when connected in series with said capacitor, a pulse forming line, and a rotary spark gap synchronized in rotation with the frequency of said alternating source, said rotary spark gap alternately permitting said capacitor to resonantly charge through said inductor from said source and to discharge through said pulse forming line when said capacitor is charged to a desired Value whereby a pulse may be formed at the output of said line.

HARRY J. WHITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,394,389 Lord Feb. 5, 1946 2,405,069 Tonks July 30, 1946 2,405,070 Tonks, et al. July 30, 1946 2,405,071 Tonks, et al July 30, 1946 2,408,824 Varela Oct. 8, 1946 2,418,126 Labin Apr. 1, 1947 OTHER REFERENCES Electric Transients," by Magnusson et al., page 76, 1st edition, published by McGraw-Hill Book Company, New York. 

